HTTP requests to the REST API are protected with HTTP Basic authentication like other REST APIs provided by Twilio. To learn more about how Twilio handles authentication, please refer to our security documentation.

In short, you will use your Twilio Account Sid as the username and your Twilio Auth Token as the password for HTTP Basic authentication.

Certain operations in the Wireless REST API – such as changing the status of a SIM – can take considerable time to complete (anywhere from a few seconds to a minute or more). These operations will return an intermediate synchronous HTTP response ('202 Accepted') while the action completes in the background.

Requests that will be processed asynchronously allow you to specify a callback URL for Twilio to notify when the request has completed. A callback is sent to your server as either an HTTP POST or GET depending on your preference. Form parameters or query string parameters sent with the callback request describe the asynchronous outcome. Callback request formats are documented with each of the relevant REST API resources.

If your initial request completes synchronously, a '200 OK', '201 Created' or '204 No Content' response will be returned and you should not expect an asynchronous callback, even if a callback URL was specified.

An event will be posted to your account's Debugger with error details if Twilio does not receive a success response from your callback URL.